MUMBAI, India — Indian authorities rounded up hundreds of people for questioning on Thursday and released photographs of two suspects in connection with the train bombings here that killed more than 180 people this week.

At the same time, a man identifying himself as a member of a newly formed chapter of Al Qaeda in the disputed territory of Kashmir, which Pakistan and India both claim, telephoned a news agency to congratulate the perpetrators. Intelligence officials said they had not verified whether the caller was authentic, and some in the government voiced their skepticism about the claim.

But the call raised the specter that groups claiming affinity with Al Qaeda had taken up the cause of the predominantly Muslim area, which has long been the scene of terrorist attacks and an Islamic insurgency, or that some Kashmir insurgents had linked themselves to Al Qaeda.

Officials in the capital, New Delhi, said they would have to investigate. "We can't take it lightly," said an intelligence official who is prohibited from speaking to the news media.

The police in Mumbai - also known as Bombay, and home to a substantial Muslim minority - combed the city overnight to search homes and detain what the city's commissioner of police, A. N. Roy, estimated to be up to 500 people.

Mr. Roy declined to specify how many remained in detention, or whether the interrogations yielded any leads. The police pointed out that no arrests had been made in connection to Tuesday's bombings.

Late Thursday, The Associated Press reported that the police had released the names and photographs of two suspects, Sayyad Zabiuddin and Zulfeqar Fayyaz, in connection with the series of eight synchronized bombs during the evening rush along a commuter train line.

The authorities remained tight-lipped about which groups could have been responsible, except to say there was a possibility that a militant organization based in Pakistan, Lashkar-e-Taiba, was involved. The police said the group could have been aided by a banned Indian organization that calls itself the Students Islamic Movement of India. Both groups have denied involvement.

Mr. Zabiuddin is suspected to have been the leader of a group of 16 militants, some of them connected to the student organization, who were arrested in May with a large cache of explosives and AK-47's in Maharashtra State, where Mumbai is located.

There have been at least four crackdowns across Maharashtra on suspected Islamist militant groups, all linked to the Kashmir cause, in the last nine months, said Mr. Roy, the police chief. Among those arrested were several affiliated with Lashkar-e-Taiba.

The group is outlawed in Pakistan, but continues to function under other guises, including, most recently, as a charity active in last October's earthquake relief efforts called Jamat ud Dawa, the police said.

The Indian Prime Minister, Manmohan Singh, who is scheduled to visit Mumbai on Friday, has said nothing directly about any organization, nor about a Pakistani hand in the attacks. Likewise, the police have presented no concrete evidence linking the bombs to any group.

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Nevertheless, the references to Lashkar-e-Taiba have prompted worrying diplomatic tensions, with the Pakistani foreign minister, Khurshid Mehmood Kasuri, lashing out late Wednesday at Indian suggestions of a Pakistani role.

"There should not be a knee-jerk reaction that everything happening in India starts in Pakistan," he told CNN.

Earlier on Wednesday, the spokesman for the Indian Foreign Ministry, Navtej Sarna, pointedly called on Pakistan to rein in terrorist organizations operating on Pakistani soil. His comments followed a suggestion by the Pakistani foreign minister, barely a day after the Mumbai bombings, that India had not done enough to resolve the Kashmir dispute. Mr. Sarna called Mr. Kasuri's comments "appalling."

The argument threatens the slow but sustained three-year peace process between the nations. "Every act of violence, and especially the kind of violence that we witnessed in Mumbai, makes it more and more difficult for the prime minister domestically to sustain the peace initiative with Pakistan," said Amitabh Mattoo, an academic who sits on the Prime Ministers Task Force on Global Strategic Development.

Attacks in Kashmir, including those on Indian tourists, have accelerated in the last few weeks. They accompany attacks in India itself.

A set of crude bombs tore through Varanasi, Hinduism's holiest city, last March. A set of synchronized explosions at two New Delhi markets and a passenger bus killed more than 50 people last October. But none of them touched off public anger toward Pakistan in the way this week's bombing has. On Thursday, the death toll from the train attack hovered at 182, with 700 injured.

The call claiming to represent Al Qaeda came at 12:15 p.m. to Current News Service, an agency based in Srinagar, the summer capital of Indian-controlled Kashmir, and a frequent recipient of calls and statements from anti-Indian militant groups there.

It lasted no more than three minutes, said the agency's chief, Abdur Rashid Rahi. The caller, who identified himself as Abu-al Hadid, spoke in polished Urdu and invited Indian Muslims to join the holy war, Mr. Rahi said, adding that the caller did not claim responsibility for the Mumbai serial bombs.

A senior government official said it should not be taken seriously. "I think it's a hoax," the official said, requesting anonymity because of the nature of the investigation. "We firmly believe it's Pakistan and not Al Qaeda."

Intelligence officials in Washington said they were investigating the claim, but they expressed skepticism that Qaeda operatives were behind the train attacks in Mumbai.

"We certainly are not ruling out the possibility that Al Qaeda was involved, given the sophistication of the attack," said one counterterrorism official in Washington, who was given anonymity to discuss intelligence matters. "But there are strong suspicions that the attacks were the work of a Pakistani militant group."